Individuals that are quadriplegic, paraplegic, or have suffered from some sort of a spinal cord injury typically rely on the use of a wheelchair to propel the user to a desired location. Some spinal cord injury patients might be inclined to choose an electric motorized wheelchair over a manual wheelchair for the minimal physical exertion required to operate such an electric wheelchair. However, motorized wheelchairs are expensive and require ramps and special vehicles to allow the wheelchair user greater mobility. That is because motorized wheelchairs are not easily folded for regular car travel. Additionally, electric wheelchairs require costly routine maintenance. Moreover, some physicians prefer to-prescribe manual wheelchairs because patients derive better cardiopulmonary effects from routine everyday use.
Manual wheelchairs are typically preferred by many wheelchair users because they are light weight, compact, low cost, and easy to use. However, many wheelchair users do not have sufficient upper body strength to traverse inclines and other rugged terrain using a standard manual wheelchair that has a 1:1 drive propulsion ratio. As such, many manual wheelchair users are limited in their scope of mobility.
Various attempts have been made to provide a two-speed or multi-speed manual wheelchair to allow users to "gear down" to a reduced gearing system such that the force required to propel the wheelchair in the lower gear is decreased. As such, even individuals with poor upper body strength may be able to maneuver a manual wheelchair on uneven terrain or inclines.
Such attempts have been made primarily through planetary gearing systems and manual lever arms. The planetary gear system, while most efficient, is mechanically complicated and can be quite expensive. The lever arm action is practical only for a small range of spinal cord injury levels due to the location of input levers. Also, the location of input lever arms compromises a user's ability to enter an exit with a wheelchair. Also, such lever arm action has a high degree of design complexity.
What is needed is a reduced cost, easily retrofit or easily manufactured, two-speed manual wheelchair that is easy to use, easy to maintain, and minimizes the overall chair width. Additionally, it is also preferred to be able to field adjust the force reduction ratio depending on a particular user's ability, such as during improvement in rehabilition or physical therapy, or a wheelchair that is used by more than one user.